Bluetooth 5 sensor device and Bluetooth 4.0 smarthphone compatibility

If the smartphone can't support BT5 features, then you can't make communication with BT 5 features.

But if you just want to implement peripheral with BT 5 capability without actually using it to connect with phones that only support BT 4, then you won't have problems.

Is it possible to develop a product which will support both Bluetooth 5 and ble 4.0? that is these device can be connect to ble 4.0 smartphones as well as Bluetooth 5 smartphones?

Yes.

Do have any reference? How we can implement it? is it just a software implementation or hardware.
Just for your information we have already developed a product using CC2541 and now client wants bluetooth 5 capability. As per our understanding for Bluetooth 5 we need to another ic ( e.g. cc2640r2f) as cc2541 does not support bluetooth 5. So is there any specific chip that support both versions or new stack software in above mentioned ic will manage both version.

The SW stack and HW is backwards compatible on CC260R2F, so you don't need to worry about it.

We will have our BLE 5 SW stack ready soon but for now, you can start the development on CC2640R2F with our SIMPLELINK_CC2640R2_SDK(supports BT4.2), which shares the same SW structure with the upcoming BLE 5 stack SW.

For more information about CC2640R2F, you can go to : www.ti.com/.../cc2640R2F
To download TI BLE stack : ti.com/ble-stack

yes thanks...! just one query ble 4.0 smartphones supports ble4.2 devices right? Sorry but just want ensure.

When we can expect bluetooth 5 stack?

The new BLE device will always work with old BLE device as long as there is no new feature used.

I don't have specific date for you, please come back to check in another 2 weeks.